Within the early 2000s, conservators at Statens Museum for Kunst (SMK) in Copenhagen found that painted white highlights on Previous Grasp drawings—works by Hans Holbein, Abraham Bloemaert, C.W. Eckersberg and others—had been darkening at an alarming charge.
Discolouration of the lead white pigment on drawings, prints and pictures has lengthy vexed conservators. However SMK, which holds one of many world’s largest drawings collections numbering round 18,000 works and relationship again to the top of the fifteenth century, noticed a chance to grasp why it was taking place and discover methods to deal with it.
“When the drawings are in that situation, they can’t be uncovered to the general public anymore as a result of they lose, in a method, their that means and their look and so they aren’t appropriate for show,” says Gianluca Pastorelli, a conservation scientist at SMK who’s a part of a multi-decade effort co-led by Niels Borring to analysis the degradation and discover methods to guard the gathering.
The problem offered a thriller as not each work, even by a single artist in a specific timeframe, reveals discolouring. This darkening can also be not often seen in oil work. Of the SMK’s 800 works drawn in chalk, charcoal or pencil and painted with lead white highlights, about half skilled a point of discolouration. An extra 200 salted prints and lithographs from Copenhagen’s Royal Library have additionally been affected.
Lead white was the pigment of alternative for its white color and distinctive qualities from antiquity onwards, till poisonous well being results drove it out of style within the twentieth century. The way it has been sourced and produced has modified over time, nevertheless it was traditionally combined with binders and brushed onto the works.
The researchers questioned whether or not sure inventive strategies or supplies had been making the affected works extra susceptible. Pastorelli’s group used superior, nondestructive imaging applied sciences, X-ray fluorescence and X-ray powder diffraction, and microsampling lead isotope evaluation to basically fingerprint the paint compounds, establish materials properties and research the chemical make-up of the darkened areas.
Their analysis confirmed that altering manufacturing strategies and the chemical composition of the pigment affected vulnerability to degradation. Additionally they discovered that chemical reactions had been changing lead white to guide sulphide, or galena, a well-known metallic-grey mineral. Micro cross sections of broken areas revealed that it was taking place most frequently on the floor. They deduced that the offender was airborne sulphur-containing compounds.
Sulphur is a air pollution byproduct—it comes from site visitors, trade and human digestive gases—and has risen precipitously because the Industrial Revolution. At SMK, a transfer to momentary storage situations was partially in charge for larger sulphur publicity ranges and noticeable darkening. However why was the early 2000s such a turning level?
“We’ve to additionally keep in mind that in 2003 to 2004, we began to have highly regarded summers and this has an influence on the quantity of air pollution that’s produced from site visitors or factories, and likewise it makes it tougher for local weather management programs inside museums and their filtering system to deal with all of the variables that should be restricted to a sure vary,” Pastorelli says. On a easy degree, warmth and accessible reactants, comparable to elevated air pollution, make chemical reactions occur quicker and extra readily.
“We imagine lead white darkening is far much less frequent on work largely as a result of many work use oil paints, and oil certainly has a robust protecting impact on lead white pigments,” Pastorelli says.
The search for a space-age resolution
Standard remedies embrace utilizing hydrogen peroxide baths or gels to lighten the darkened highlights, however carry threat of harm to the supplies within the work and chemically create a brand new compound, which isn’t perfect in conservation. “It’s like an old-school most cancers drug—it treats, nevertheless it additionally destroys,” says Tomas Markevicius, an artwork conservator and founding father of the Moxy Mission analysis initiative.
Markevicius and his group, which incorporates Pastorelli, are finding out a wholly new method to this conservation problem—using atomic oxygen. In Could, at a convention in Perugia, he offered the primary ever use of atomic oxygen to reverse lead white darkening—with out water, acids or contact—on lab mockups. He calls it “a serious breakthrough in each chemistry and artwork conservation”.
If it sounds area age, that’s as a result of it’s. Atomic oxygen is a extremely reactive type of oxygen present in low Earth orbit that readily interacts with chemical compounds round it. Nasa scientists Sharon Miller and Bruce Banks researched how this disruptive gasoline would influence spacecraft exteriors and later studied its use to scrub gadgets of cultural heritage.
Upon contact with atomic oxygen, natural supplies like soot, stains and varnishes launch into the air. “They get transformed to carbon monoxide and carbon dioxide and depart as a gasoline, so that they don’t depart residue on the floor,” Miller says.
She and Banks had been in a position to check it out on an unlikely contaminant. At a 1997 occasion organised for the style model Chanel on the Andy Warhol Museum in Pittsburgh, a reckless visitor defaced Warhol’s hand-painted Bathtub (1961) with a lipstick-laden kiss. Standard remedies didn’t take away the make-up. Miller and Banks employed an atmospheric oxygen beam for greater than 5 hours that eliminated the smudge but additionally among the underlying grime and a skinny paint layer.
Markevicius’s Moxy group is creating atomic oxygen expertise as a part of a inexperienced cluster in cultural heritage backed by the European Union to develop sustainable applied sciences. They intention to supply a lab-scale prototype by late 2026 and are rigorously testing mock-ups and bodily delicate supplies with various contaminants to optimise protocols.
For now, SMK is making certain that its local weather management and air-filtering programs work effectively, however it’s not taking motion to lighten the darkened highlights in affected works, as a result of there may be presently no protected method. “It’s a robust driver to develop such applied sciences that will have the least influence upon these extremely priceless but additionally extremely fragile constructions, that are distinctive,” Markevicius says.
